UPDATE 2.30PM: WHILE the image of a puppy travelling in cage on top of a car on the Bruce Hwy has attracted immense outrage, an RSPCA spokesman has said it is not an illegal action.

According to RSPCA spokesman Michael Beatty, the situation was similar to that of a dog in the back of a ute.

While there were concerns about the heat, he said as long as the drivers were monitoring the dogs condition and making sure it was at no risk, then putting the cage on top of the car was not against the law.

However, RSPCA Queensland was still interested in gathering more information about the incident.

EARLIER 9AM: HOT sun, 100kmh speeds and excessive noise.

These were the conditions a young puppy was subjected to over the weekend when it was spotted in an open cage strapped to the roof of a car barrelling down the Bruce Hwy towards Gympie.

The RSPCA is now trying to identify the driver of the car, which was seen on Friday and Saturday between Gin Gin and Maryborough and may have driven through Gympie on its way south.

According to one witness who posted online, the puppy looked to be about four months old.

"I imagine (it was) terrified as it was subject to H'Way noise and over 100kph wind without shelter at all... what would this do to a human?" they said.

"All up we observed this for about 115Ks over well an hour and a half."

The RSPCA are seeking any further information on the car.

"If anyone has first hand information on other sightings please get in touch with us to help further this case," the organisation said on their RSPCA Queensland Facebook page.

They also said it was important people not share the registration plate of the car if they know who it belongs to.

"Sharing the registration number can reduce our ability to prosecute to the full extent," they said.